Loripsum.net has an API to generate placeholder text to insert it in whatever software/webapp you want.
Just do a GET request on loripsum.net/api, to get some placeholder text. You can add extra parameters to specify the output you're going to get. Say, you need 10 short paragraphs with headings, use loripsum.net/api/10/short/headers. All of the possible parameters are:
(integer) - The number of paragraphs to generate.
short, medium, long, verylong - The average length of a paragraph.
decorate - Add bold, italic and marked text.
link - Add links.
ul - Add unordered lists.
ol - Add numbered lists.
dl - Add description lists.
bq - Add blockquotes.
code - Add code samples.
headers - Add headers.
allcaps - Use ALL CAPS.
prude - Prude version.
plaintext - Return plain text, no HTML.
Most generators only output paragraphs of about the same length. Sometimes you need lists, headings, long paragraphs, short paragraphs, etc. The website/magazine that you're designing probably isn't going to be filled with uniform paragraphs, so your placeholder text should reflect that.